Controller for a hydraulic press and method for the operation thereof

ABSTRACT

The invention relates to a controller for a hydraulic press, comprising a pressing cylinder ( 1 ), a reservoir ( 2 ), a valve group ( 3 ), a pressure medium reservoir ( 7 ) and a hydraulic pump ( 6 ), connected together by means of a cylinder line ( 4 ), a reservoir line ( 5 ) and a tank line ( 8 ). According to the invention, a pressure converter ( 9 ) is arranged on the valve group ( 3 ), which may operate as a pressure amplifier or pressure reducer. The particular mode of action of said controller is achieved whereby the valve group ( 3 ) comprises a pre-press valve ( 11 ), a low-pressure chamber outlet valve ( 12 ), a low-pressure chamber inlet valve ( 13 ), a main press valve ( 14 ), a closing valve ( 15 ), a pressure release valve ( 16 ) and a 3-way valve ( 17 ), which may be operated by a particular control sequence. Said invention is applicable in hydraulic presses and of particular advantage in presses for the forming of ceramic pieces such as tiles.

PRIORITY CLAIM

This is a U.S. national stage application of application No.PCT/IB/01527, filed on Aug. 24, 2001. Priority is claimed to thatapplication and to application No. 1826/00, filed Sep. 20, 2000 inSwitzerland.

FIELD OF THE INVENTION

The present invention relates to a controller for a hydraulic apparatus,specifically to a controller for a hydraulic press machine and a methodof operating same.

BACKGROUND OF THE INVENTION

Hydraulic presses are used when workpieces are to be formed or reformed.Hydraulic presses are also used for cutting operations. The requiredforce of the hydraulic press depends on the workpiece. In the ceramicindustry, presses having a pressing force of 20,000 kN or more are used.In this case, with a view to efficient manufacture, the cycle time for apressing operation should be as short as possible. Cycle sequences of 20strokes per minute are a guideline. The pressing force and the cycletime determine the energy to be expended, that is to say, in hydraulicpresses, the power of pumps and of electric motors driving these pumps.In hydraulic presses according to the prior art, accumulators are alsoused, such as pressure medium accumulators or flywheels.

DE A1-43 20 213 discloses a hydraulic press that includes a feed circuitof the hydraulic pressing cylinder. A pressure medium accumulator ischarged during the return stroke of the press and is utilized for thedrive during the feed of the pressing die. Energy can thus be saved inthe main drive.

JP-A-63 256 300 discloses a press which is operated with a multistagepressure converter. After a first pressing operation at low pressure,the hydraulic oil is discharged into the tank. A second pressingoperation then takes place at high pressure. Energy recovery isconsequently not possible in this case.

A hydraulic drive system for a press in the relevant field is disclosedin U.S. Pat. No. A-5,852,933 and DE A1-44 36 666. It contains alow-pressure and a high-pressure circuit. In this, there are threehydrostatic machines, two of which are coupled mechanically. In order tomake satisfactory operation possible, these machines must be adjustablein terms of their absorption volume or delivery volume. This entailsconsiderable costs. The system described here can be employed only whenthe press has differential cylinders or synchronous cylinders.

DE-A1-43 08 344 discloses the principle of secondary regulation forregulating the drive of a hydraulic press. The various movements of thepress ram are combined with one another in such a way that the pressurenetwork operates in a closed circuit, the maximum system pressure beingdetermined by the pressure medium accumulator.

DE-A1-43 08 344 discloses that the hydraulic oil is definitelycompressible also plays a part in the regulation of a hydraulic press.This has an effect in a press cycle during both compression anddecompression and constitutes a source of losses.

The prior art has continued largely to ignore the fact that themechanical parts of the press also absorb energy due to the elasticdeformation of their components. This energy has to be expended duringthe closing operation of the press. This energy is not recovered duringthe opening operation.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a hydraulic presswith the hydraulic control such that the total energy requirement isreduced without an associated increase in apparatus expenditures.Preferably, the control is in this case also to be capable of being usedin a press with plunger cylinders.

Other objects and features of the present invention will become apparentfrom the following detailed description considered in conjunction withthe accompanying drawings. It is to be understood, however, that thedrawings are designed solely for purposes of illustration and not as adefinition of the limits of the invention, for which reference should bemade to the appended claims. It should be further understood that thedrains are not necessarily drawn to scale and that, unless otherwiseindicated, they are merely intended to conceptually illustrate thestructures and procedures described herein.

PCT Publication Sheet, Int'l Preliminary Examination Report, WrittenOpinion, Int'l Search Report

BRIEF DESCRIPTION OF THE DRAWINGS

In the Drawings:

FIG. 1 is a schematic diagram of hydraulic system of a press control.

FIGS. 2 to 6 are illustrations of the hydraulic system showingindividual steps within a cycle.

FIG. 7 shows a diagram of a design variant of the press control.

DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS

In FIG. 1, a press cylinder 1 is connected to a reservoir 2 for thehydraulic medium. A valve group 3 includes a series of valves.

The hydraulic medium is conveyed between the press cylinder 1 and thevalve group 3 via a cylinder line 4.

An accumulator line 5 is connected to the valve group 3. A hydraulicpump 6 delivers hydraulic medium into this accumulator line 5 and isdriven by an electric motor, which is not illustrated here. A pressuremedium accumulator 7 is connected to the accumulator line 5 which alsoruns within the valve group 3. That is to say, also, the hydraulic pump6 is capable of delivering the hydraulic medium into the pressure mediumaccumulator 7. A one-way valve, not illustrated, may be arranged in theline segment between the hydraulic pump 6 and the accumulator line 5, inorder to relieve the hydraulic pump 6 of the pressure prevailing in thepressure medium accumulator 7, when the hydraulic pump 6 is not running.

A tank line 8 leads from the valve group 3 to the reservoir 2. Valvegroup 3 is connected to a pressure converter 9 which acts as a pressureintensifier and also as a pressure reducer. The pressure converter 9 hasa piston 9K which is displaceable within a cylinder 9Z. Piston 9Kseparates a low-pressure space 9.1 having a large effective crosssection from a high-pressure space 9.2 having a small effective crosssection. In order to obtain the smaller effective cross section, apiston rod 9S connected to the piston 9K is located in the high-pressurespace 9.2. The effective ratio in terms of pressure and volume flow isdetermined by the cross sections of the two pressure spaces 9.1 and 9.2.The cross sectional area is determined, for the low-pressure space 9.1,for the inside diameter of the cylinder 9Z according toA _(9.1)=¼*d _(9Z) ²*πand, for the high-pressure space 9.2, by the difference between theinside diameters of the cylinder 9Z and of the piston rod 9S accordingtoA _(9.2)=¼*(d _(9Z)-d _(9S))²*π

A_(9.1) is in this case the hydraulically effective cross sectional areaof the low-pressure space 9.1, A_(9.2) is that of the high-pressurespace 9.2, d_(9Z) is the inside diameter of the cylinder 9Z and d_(9S)is the diameter of the piston rod 9S.

The pressure ratio of the pressure converter 9 and, correspondingly,also the ratio of the volume flows is therefore determined byA_(9.1):A_(9.2). The ratio A_(9.1):A_(9.2) is, for example, 2:1. Theposition of the piston 9K is detected by means of a displacementtransducer 9W.

The low-pressure space 9.1 is connected to a pressure converterlow-pressure line 10.1 of the valve group 3. Located on this pressureconverter low-pressure line 10.1 are three switching valves: aprepressing valve 11, the second connection of which is connected to thecylinder line 4; a low-pressure chamber outlet valve 12, the secondconnection of which is connected to the reservoir 2 via the tank line 8;and a low-pressure chamber inlet valve 13, the second connection ofwhich is connected to the accumulator line 5 and consequently also tothe pressure medium accumulator 7.

The high-pressure space 9.2 is connected to a pressure converterhigh-pressure line 10.2 of the valve group 3. Valves are likewiselocated on this pressure converter high-pressure line 10.2: a mainpressing valve 14, the second connection of which is connected to thecylinder line 4, and a stop valve 15, the second connection of which isconnected to the accumulator line 5 and consequently also to thepressure medium accumulator 7.

A pressure relief valve 16 lies between the cylinder line 4 and the tankline 8. Moreover, a third valve, three-way valve 17, with a precedingone-way valve 18, is connected to the pressure converter high-pressureline 10.2. The three-way valve 17 is also connected to the accumulatorline 5 and consequently also to the pressure medium accumulator 7 and,with its further connection, to the lank line 8 and therefore to thereservoir 2. The line segment 19 between the one-way valve 18 and thethree-way valve 17 is a pressing line. The one-way valve 18 is, infunctional terms, a backflow stop valve. The functioning of the variousvalves 11, 12, 13, 14, 15, 16 and 17 is described in detail hereafterwith reference to FIGS. 2 through 6. The valves can be activatedelectrically and are controlled by a control apparatus 20. For clarity,connecting lines from the control apparatus 20 to the valves 11, 12, 13,14, 15, 16 and 17 are not shown in the figures.

The schematic diagram of the hydraulic system illustrates only theelements essential to the invention, there also being, in addition, apress safety lowering and pullback control 21 which is necessary for thereliable operation of the press cylinder 1 but is irrelevant in terms ofthe invention. A pressure transducer 22 which detects the pressure inthe cylinder line 4 is also necessary.

The electric connections between the control apparatus 20, displacementtransducer 9W, pressure transducer 22, press safety lowering andpullback control 21 and further safety-relevant elements on the pressare also not shown for the sake of clarity.

A first phase of the press operation, to be precise the buildup of theadmission pressure, is described below with reference to FIG. 2. Thepress cylinder 1 is filled in the usual way with hydraulic medium fromthe reservoir 2, this being indicated by an arrow. As a result, theupper pressing die is lowered and consequently the mold is closed. Thepiston 9K is at the same time located in an upper position in thevicinity of its upper end position A.

The three-way valve 17 is then activated in such a way that it releasesthe throughflow from the connection of the accumulator line 5 to theconnection of the pressing line 19. The activation of the three-wayvalve 17 using its electrically operated drive is marked in FIG. 2 insolid black. Opening of the three-way valve 17 permits hydraulic mediumbe flow from the pressure medium accumulator 7 via said three-way valve17 via the pressing line 19, via the one-way valve 18 (which necessarilyopens on account of the pressure of the hydraulic medium) and via thepressure converter high-pressure line 10.2 into the high-pressure space9.2 of the pressure converter 9. This is indicated in FIG. 2 by thearrows.

At the same time, the prepressing valve 11 is also activated. Theactivation by its electrically operated drive is marked in solid black.Consequently, hydraulic medium can flow out of the low-pressure space9.1 via the pressure converter low-pressure line 10.1 via theprepressing valve 11 and the cylinder line 4 into the press cylinder 1.Owing to the area ratio A_(9.2) to A_(9.1), the pressure converter 9then acts as a pressure reducer, the quantity of hydraulic medium beingincreased according to the area ratio A_(9.2) to A_(9.1). When the arearatio A_(9.2) to A_(9.1), amounts, for example, to 1:2, the pressure isreduced in the ratio of 1:2 by means of the pressure converter 9, butthe quantity of hydraulic medium is increased in the ratio of 1:2.

Due to the flow of the hydraulic medium, the piston 9K is moved in thedirection of B.

It should also be noted that the three-way valve 17 is a proportionallycontrollable valve. That is, the drive of the three-way valve 17 is, forexample, a proportional magnet, so that the pressure in the pressingline 9 and in the pressure converter high-pressure line 10.2 andtherefore also the pressure in the pressure converter low-pressure line10.1, in the cylinder line 4 and in the press cylinder 1 can becontrolled or regulated.

When the desired admission pressure is reached, as detected by thepressure transducer 22, the detection transmitted from the latter to thecontrol apparatus 20 and thus noted by the control apparatus 20, thecontrol apparatus 20 causes the three-way valve 17 and the prepressingvalve 11 to be closed.

Subsequently, then, the pressure relief valve 16 is activated and thusopened causing a loss of pressure in the press cylinder 1 and in thecylinder line 4. This is detected by the pressure transducer 22.Hydraulic medium consequently flows from the press cylinder 1 and thecylinder line 4 via the pressure relief valve 16 and through the tankline 8 to the reservoir 2. When the pressure transducer 22 determinesthat the press cylinder 1 and the cylinder line 4 are pressureless, thepressure relief valve 16 is closed again.

It may be advantageous to add a further phase in the buildup of anadmission pressure. This is carried out in the way described above, butin this case with a higher admission pressure which is reached by meansof an appropriately modified activation of the three-way valve 17. Thisphase may take place while the upper die, not shown, lies on theworkpiece, likewise not shown. It may also be advantageous, however, toraise the upper die slightly.

After the phase for building up the admission pressure or admissionpressures, the piston 9K is located, within the cylinder 9Z, near thelower end at B. This is detected by the displacement transducer 9W. Thisposition is necessary so that the main pressing pressure required cansubsequently be generated.

The next phase of press operation, the buildup of the main pressingpressure, then follows. This is described below with reference to FIGS.3 and 4.

FIG. 3 shows the first step of this phase. This figure, then, againillustrates the activated valves by means of a solid black marking ofthe electric drives, and the flow of the hydraulic medium is indicatedby arrows next to the lines.

As can be seen from FIG. 3, therefore, in this case the stop valve 15and the main pressing valve 14 are activated. The stop valve 15 and themain pressing valve 14 are then opened. Valves 14, 15 are advantageouslyelectrically activatable OPEN/SHUT valves. The prepressing valve 11,low-pressure chamber inlet valve 13, low-pressure chamber outlet valve12 and pressure relief valve 16 are advantageously also electricallyactivatable OPEN/SHUT valves.

Activating stop valve 15 and main pressing valve 14 causes the flow ofhydraulic medium from the pressure medium accumulator 7 via theaccumulator line 5, through the stop valve 15 and the main pressingvalve 14 and through the cylinder line 4 to the press cylinder 1. Thus,in the press cylinder 1, a pressure is built up which is predetermined,but corresponds at most to the pressure in the pressure mediumaccumulator 7.

FIG. 4 shows the second step of the phase of building up the mainpressing pressure. In this case, the low-pressure chamber inlet valve 13and the main pressing valve 14 are activated by the electric drives ofthe valves 13, 14 that is to say open. This is indicated using solidblack markings as in the previous figures. The flow of hydraulic mediumwhich is established is again identified by arrows next to the lines.

Thus, the hydraulic medium then flows from the pressure mediumaccumulator 7 through the accumulator line 5 and the open low-pressurechamber inlet valve 13 and through the pressure converter low-pressureline 10.1 into the low-pressure space 9.1 of the pressure converter 9.The pressure prevailing in the pressure medium accumulator 7 alsothereby arises in the low-pressure space 9.1. As a result of the arearatio A_(9.2) to A_(9.2), a higher pressure simultaneously arises in thehigh-pressure space 9.2, said pressure therefore being twice as high asthe pressure in the pressure medium accumulator 7 in the case of analready mentioned area ratio A_(9.2) to A_(9.1) of 1:2. Since, however,the main pressing valve 14 is now also open, a likewise high pressure isbuilt up in the press cylinder 1. At the conclusion of this phase ofpress operation, therefore, the pressure in the press cylinder 1 istwice as high as the pressure in the pressure medium accumulator 7 underthe given conditions.

The buildup of this pressure in the press cylinder 1 is tracked by thepressure transducer 22. As soon as the desired pressure is reached, thelow-pressure chamber inlet valve 13 and the main pressing valve 14 areclosed again. It goes without saying that this pressure buildup isassociated with a flow of hydraulic medium from the pressure mediumaccumulator 7 into the low-pressure space 9.1 and from the high-pressurespace 9.2 via the cylinder line 4 to the press cylinder 1, with theresult that the piston 9K is also displaced in the direction of A. Owingto the area ratio A_(9.2) to A_(9.1), the quantity of hydraulic mediumflowing out from the high-pressure space 9.2 is in this case, under thegiven conditions of an area ratio A_(9.2) to A_(9.1) of 1:2, only halfas large as the quantity of hydraulic medium which flows from thepressure medium accumulator 7 into the low-pressure space 9.1.

The press then reaches its maximum pressure and performs the pressing.Under the effect of this pressure, the stresses in the components of thepress are also at the maximum values. Since the components are deformedelastically, energy is therefore stored in these components. A furtherenergy potential is the compressible hydraulic medium volume in thepress cylinder 1, press line 4, pressure converter high-pressure line10.2 and high-pressure space 9.2 of the pressure converter 9.

A phase of relief with stress breakdown and decompression thensubsequently takes place. This phase occurs in three steps, the firsttwo of which are illustrated in FIGS. 5 and 6.

The first step is shown in FIG. 5. The main pressing valve 14 and thestop valve 15 are then open, this is illustrated by a solid blackmarking of the drives of the valves 14, 15 in a similar way to theprevious figures.

The hydraulic medium can then flow from the press cylinder 1 to thepressure medium accumulator 7, at the same time following the paththrough the cylinder line 4, the main pressing valve 14, the stop valve15 and accumulator line 5. The flow occurs because the pressure in thepress cylinder 1 is higher than it is in the pressure medium accumulator7. The first step lasts until the pressures in the press cylinder 1 andin the pressure medium accumulator 7 are equal. That is to say, however,also that a considerable part of the energy stored in the components ofthe press is recovered, in that the pressure in the pressure mediumaccumulator 7 is increased. This is an advantage of the controlleraccording to the present invention and of the method for the operationthereof.

The second step of the relief phase is described with reference to FIG.6, again the drives of the activated valves being illustrated as solidblack markings, and the flow of hydraulic medium being is identified byarrows at the lines.

This second step serves for preparing the next press cycle. For this,the pressure converter 9 has to assume a predetermined position in thedirection of B. The volume still remaining in the low-pressure space 9.1of the pressure converter is then such that the admission pressures forthe next work cycle can be provided by means of this volume. A check asto whether this is so can be made by means of the displacementtransducer 9W. If this is not so, the residual pressure prevailing inthe press cylinder 1, in the cylinder line 4 and in the pressureconverter high-pressure line 10.2 is utilized, by the opening of themain pressing valve 14 and the low-pressure chamber outlet valve 12, inorder to bring the piston 9K of the pressure converter 9 into thedesired position.

This desired position is illustrated in FIG. 6. Therein, thehigh-pressure space 9.2 is also already filled again with pressurizedhydraulic medium, so that no hydraulic medium at all has to be extractedfrom the pressure accumulator 7 for filling purposes. This signifies afurther energy saving. The hydraulic medium displaced out of thelow-pressure space 9.1 during the movement of the piston 9K passes viathe low-pressure chamber outlet valve 12 through the tank line 8 intothe reservoir 2. When the piston 9K has reached the desired position,this being determined by the displacement transducer 9W, thelow-pressure chamber outlet valve 12 and the main pressing valve 14 areclosed again.

Subsequently, in the third step, the residual pressure in the presscylinder 1 and in the cylinder line 4 is released by opening of thepressure relief valve 16. Thus, under the effect of the residualpressure, hydraulic medium flows from the press cylinder 1 through thecylinder line 4, the pressure relief valve 16 and the lank line 8 intothe reservoir 2. The flow ceases as soon as the residual pressure in thepress cylinder 1 is lost completely and the pressure will be equivalentto the ambient pressure. The pressure relief valve 16 is then closedagain.

At the same time, however, the pressure in the high-pressure space 9.2and in the pressure converter high-pressure line 10.2 is maintained.This pressure can be utilized during the next press cycle, thusresulting in an energy saving, since the pressure does not have to bebuilt up anew.

FIG. 7 shows an embodiment of the press control according to the presentinvention. Compared with the first embodiment of FIG. 1, the only changeis that the pressure converter 9′ is of a different type from thepressure converter 9 shown in FIGS. 1 to 6.

The pressure converter 9′ includes a first pump 23 having a shaft 24that is coupled rigidly to a second pump 25, so that the shaft 24 iscommon to both pumps 23, 25. The first pump 23 is connected to thepressure converter low-pressure line 10.1. That side of the pump 23 actsas a low-pressure space 9.1. Pump 23 is also connected to a tank 26. Thesecond pump 25 is connected to the pressure converter high-pressure line10.2 to act as a high-pressure space 9.2, and also is connected tolikewise to the tank 26.

The two pumps 23, 25 are not driven by a motor, but, by virtue of therigid connection, act in each case as a unit consisting of pump and ofhydraulic motor, i.e. a single-stage pressure converter 9, as oneskilled in the art would recognize. This combination of the two pumps23, 25 takes effect as a pressure converter in that the specificdelivery volume, that is to say the volume per revolution, is different.This is illustrated in FIG. 7 schematically by the different size of thepumps 23, 25. Thus, for example, this ratio amounts to 2:1. This alsooccurs in that the areas effective in the two pumps 23, 25 in thedelivery of the hydraulic medium through the latter correspond to theareas A_(9.1) and A_(9.2) according to the first embodiment.Correspondingly, the pressure converter 9′ behaves in exactly the sameway as the pressure converter 9 during the different phases of pressoperation which are illustrated in FIG. 2 to 6 and described withreference to these figures. During the above-mentioned first phase ofpress operation, for example, the pressure converter 9′ acts as apressure reducer while the second pump 25 operates as a hydraulic motorand drives the first pump 23. In action as a pressure intensifier, thefirst pump 23 acts as a hydraulic motor which drives the second pump 25.The individual phases and their steps of a press cycle correspond tothose of the first embodiment.

It is also advantageous, in this case, that a displacement transducer 9Wis not required and the pressure converter 9′ does not have to assume apredetermined position for the preparation of the next press cycle. Thissimplifies the control method.

Despite the seemingly simple construction of the controller according tothe present invention, energy from individual pressing steps can berecovered by means of this controller. Thus, even the energy storedelastically in the press, in the workpiece and in the compressiblehydraulic oil is recovered. At the same lime, the controller manageswithout costly structural elements, such as adjustable pumps.

It was found by means of tests that, by virtue of the controlleraccording to the present invention, a considerable amount of energysavings can be achieved as compared with those known in the field of theart. The energy saving may definitely amount to around 40%.

The present invention may, in principle, be utilized to great advantagein hydraulic presses of various types for various fields of use. Thepress may in this case be equipped with differential cylinders,synchronous cylinders or else plunger cylinders. It is particularlyadvantageous if the controller according to the present invention isused in presses for the shaping of ceramic parts, such as tiles.

Thus, while there have been shown and described and pointed outfundamental novel features of the invention as applied to a preferredembodiment thereof, it will be understood that various omissions andsubstitutions and changes in the form and details of the devicesillustrated, and in their operation, may be made by those skilled in theart without departing from the spirit of the invention. For example, itis expressly intended that all combinations of those elements and/ormethod steps which perform substantially the same function insubstantially the same way to achieve the same results are within thescope of the invention. Moreover, it should be recognized thatstructures and/or elements and/or method steps shown and/or described inconnection with any disclosed form or embodiment of the invention may beincorporated in any other disclosed or described or suggested form orembodiment as a general matter of design choice. It is the intention,therefore, to be limited only as indicated by the scope of the claimsappended thereto.

1. A controller for a hydraulic press, the hydraulic press including apress cylinder (1), a reservoir (2) for a pressure medium, a pressuremedium accumulator (7), a hydraulic pump (6), operably connected to eachother by a first plurality of connections, the first plurality ofconnections including a cylinder line (4) operably connecting the presscylinder (1), an accumulator line operably connected to the pressuremedium accumulator, and a tank line; the controller comprising: apressure converter (9,9′) for altering a pressure of a pressure medium,the pressure converter (9,9′) being a single-stage pressure converter,the converter comprising a cylinder (9Z), a piston rod (9S) for reducinga volume of the cylinder (9Z), a piston (9K) displaceable in thecylinder (9Z) for dividing the cylinder (9Z) into a low-pressure space(9.1) and a high-pressure space (9.2) separated from one another by thepiston (9K) wherein the cross-sectional area (A_(9.1)) of thelow-pressure space (9.1) is larger than the cross-sectional area(A_(9.2)) of the high-pressure space (9.2); a control apparatus (20); avalve group (3) operably connected to the press cylinder of thehydraulic press by the cylinder line of the first plurality ofconnections, the valve group (3) and the accumulator (7) being operablyconnected to one another by the accumulator line (5) of the firstplurality of connections, and the valve group (3) being operablyconnected to the reservoir (2) by the tank line of the first pluralityof connections; a second plurality of connections for operablyconnecting the control apparatus (20) to the valve group (3); and athird plurality of connections for operably connecting the valve group(3) to the pressure converter (9,9′), wherein the valve group (3)further comprises a prepressing valve (11) operably connected to thecylinder line (4), a low-pressure chamber inlet valve (13) operablyconnected to the accumulator line (5), a low-pressure chamber outletvalve (12) operably connected to the tank line (8), a main pressingvalve (14) operably connected to the cylinder line (4), a one-way valve(18), a three-way valve (17) operably connected to the one-way valve(18), to the accumulator line (5), and the tank line (8), and a stopvalve (15) operably connected to the accumulator line (5); and whereinthe third plurality of connections further comprises a pressureconverter low-pressure line (10.1) for operably connecting thelow-pressure space (9.1) to the prepressing valve (11), the low-pressurechamber inlet valve (13), and the low-pressure chamber outlet valve(12), and a pressure converter high-pressure line (10.2) for operablyconnecting the high-pressure space (9.2) to the main pressing valve(14), the stop valve (15), the one-way valve (18) and a pressing line(19) to the 3-way valve (17), the second connection of which lies on theaccumulator line (5) and the third connection of which lies on the tankline (8).
 2. The controller of claim 1, wherein the 3-way valve (17) iscontrollable proportionally.
 3. The controller of claim 1, wherein thevalve group (3) further comprises a pressure relief valve (16) operablyconnected the cylinder line (4) and the tank line (8).
 4. The controllerof claim 3, wherein the prepressing valve (11), the low-pressure chamberinlet valve (13), the low-pressure chamber outlet valve (12), the mainpressing valve (14), the stop valve (15) and the pressure relief valve(16) are electrically controllable OPEN/SHUT valves.
 5. A controller fora hydraulic press, the hydraulic press including a press cylinder (1), areservoir (2) for a pressure medium, a pressure medium accumulator (7),a hydraulic pump (6), operably connected to each other by a firstplurality of connections, the first plurality of connections including acylinder line (4) operably connecting the press cylinder (1), anaccumulator line operably connected to the pressure medium accumulator,and a tank line; the controller comprising: a pressure converter (9,9′)for altering a pressure of a pressure medium, the pressure converter(9,9′) being a single-stage pressure converter, wherein the pressureconverter (9′) comprises: a first pump (23) with a high specificdelivery volume including a first side of the first pump (23) for actingas a low-pressure space (9.1), a second pump (25) with a low specificdelivery volume including a first side of the second pump (25) foracting as a high-pressure space (9.2), and a shaft (24) for rigidlyconnecting a second side of the first pump to a second side of thesecond pump; a control apparatus (20); a valve group (3) operablyconnected to the press cylinder of the hydraulic press by the cylinderline of the first plurality of connections, the valve group (3) and theaccumulator (7) being operably connected to one another by theaccumulator line (5) of the first plurality of connections, and thevalve group (3) being operably connected to the reservoir (2) by thetank line of the first plurality of connections; a second plurality ofconnections for operably connecting the control apparatus (20) to thevalve group (3); and a third plurality of connections for operablyconnecting the valve group (3) to the pressure converter (9,9′), whereinthe valve group (3) further comprises a prepressing valve (11) operablyconnected to the cylinder line (4), a low-pressure chamber inlet valve(13) operably connected to the accumulator line (5), a low-pressurechamber outlet valve (12) operably connected to the tank line (8), amain pressing valve (14) operably connected to the cylinder line (4), aone-way valve (18), a three-way valve (17) operably connected to theone-way valve (18), to the accumulator line (5), and the tank line (8),and a stop valve (15) operably connected to the accumulator line (5);and wherein the third plurality of connections further comprises apressure converter low-pressure line (10.1) for operably connecting thelow-pressure space (9.1) to the prepressing valve (11), the low-pressurechamber inlet valve (13), and the low-pressure chamber outlet valve(12), and a pressure converter high-pressure line (10.2) for operablyconnecting the high-pressure space (9.2) to the main pressing valve(14), the stop valve (15), the one-way valve (18) and a pressing line(19) to the 3-way valve (17), the second connection of which lies on theaccumulator line (5) and the third connection of which lies on the tankline (8).
 6. The controller of claim 5, wherein the 3-way valve (17) iscontrollable proportionally.
 7. The controller of claim 6, wherein theprepressing valve (11), the low-pressure chamber inlet valve (13), thelow-pressure chamber outlet valve (12), the main pressing valve (14),the stop valve (15) and the pressure relief valve (16) are electricallycontrollable OPEN/SHUT valves.
 8. The controller of claim 5, wherein thevalve group (3) further comprises a pressure relief valve (16) operablyconnected the cylinder line (4) and the tank line (8).
 9. A method ofcontrolling a hydraulic press, the hydraulic press including a presscylinder (1), a reservoir (2) for a pressure medium, a pressure mediumaccumulator (7), a hydraulic pump (6), operably connected to each otherby a first plurality of connections; the controller including a pressureconverter (9,9′) for altering a pressure of a pressure medium; a controlapparatus (20); a valve group (3) operably connected to the hydraulicpress; a second plurality of connections for operably connecting thecontrol apparatus (20) to the valve group (3); and a third plurality ofconnections for operably connecting the valve group (3) to the pressureconverter (9,9′), wherein the valve group (3) comprises a prepressingvalve (11) operably connected to the cylinder line (4), a low-pressurechamber inlet valve (13) operably connected to the accumulator line (5),a low-pressure chamber outlet valve (12) operably connected to the tankline (8), a main pressing valve (14) operably connected to the cylinderline (4), a one-way valve (18) a three-way valve (17) operably connectedto the one-way valve (18), to the accumulator line (5), and the tankline (8), and a stop valve (15) operably connected to the accumulatorline (5), and wherein the third plurality of connections comprises apressure converter low-pressure line (10.1) for operably connecting thelow-pressure space (9.1) to the prepressing valve (11), the low-pressurechamber inlet valve (13), and the low-pressure chamber outlet valve(12), and a pressure converter high-pressure line (10.2) for operablyconnecting the high-pressure space (9.2) to the main pressing valve(14), the stop valve (15), the one-way valve (18) and a pressing line(19) to a 3-way valve (17), the second connection of which lies on theaccumulator line (5) and the third connection of which lies on the tankline (8) the method comprising the step of operating the pressureconverter (9; 9′) as a pressure intensifier or as a pressure reducer by(a) activating the three-way valve (17) and the prepressing valve (11)to force the pressure converter (9; 9′) to act as a pressure reducer andto generate a first level of a pressure in the press cylinder (1); (b)activating the stop valve (15) and the main pressing valve (14) togenerate a predetermined second level of the pressure in the presscylinder (1), the second level of the pressure being less than or equalto a pressure in the pressure medium accumulator (7); (c) activating themain pressing valve (14) and the low-pressure chamber inlet valve (13)to force the pressure converter (9; 9′) to act as a pressure intensifierand to generate a third level of the pressure in the press cylinder (1),the third level of the pressure being greater than the pressure in thepressure medium accumulator (7); (d) activating the main pressing valve(14) and of the stop valve (15) to reduce the pressure in the presscylinder (1) to a fourth level of the pressure, the fourth levelsubstantially equal to the pressure in the pressure medium accumulator(7), and (e) activating the pressure relief valve (16) to reduce thepressure in the press cylinder (1) to the ambient pressure.
 10. Themethod of claim 9 further comprising between step (d) and (e) the stepsof: determining if another press cycle is desired; activating the mainpressing valve (14) and the low-pressure chamber outlet valve (12) tobring the piston (9K) of the pressure converter (9) a predeterminedposition and repeating steps (a)-(d).
 11. The method of claim 9 furthercomprising after step (a) the steps of: activating the three-way valve(17) in a modified activation and activating the prepressing valve (11)to force the pressure converter (9; 9′) to act as a pressure reducer andto generate an increase in the first level of the pressure in the presscylinder (1).
 12. A method of controlling a hydraulic press for theshaping of ceramic parts, the hydraulic press including a press cylinder(1), a reservoir (2) for a pressure medium, a pressure mediumaccumulator (7), a hydraulic pump (6), operably connected to each otherby a first plurality of connections; the controller including a pressureconverter (9,9′) for altering a pressure of a pressure medium; a controlapparatus (20); a valve group (3) operably connected to the hydraulicpress; a second plurality of connections for operably connecting thecontrol apparatus (20) to the valve group (3); and a third plurality ofconnections for operably connecting the valve group (3) to the pressureconverter (9,9′), the valve group (3) comprising: a prepressing valve(11) operably connected to the cylinder line (4), a low-pressure chamberinlet valve (13) operably connected to the accumulator line (5), alow-pressure chamber outlet valve (12) operably connected to the tankline (8), a main pressing valve (14) operably connected to the cylinderline (4), a one-way valve (18) a three-way valve (17) operably connectedto the one-way valve (18), to the accumulator line (5), and the tankline (8), and a stop valve (15) operably connected to the accumulatorline (5); and wherein the third plurality of connections furthercomprises a pressure converter low-pressure line (10.1) for operablyconnecting the low-pressure space (9.1) to the prepressing valve (11),the low-pressure chamber inlet valve (13), and the low-pressure chamberoutlet valve (12), and a pressure converter high-pressure line (10.2)for operably connecting the high-pressure space (9.2) to the mainpressing valve (14), the stop valve (15), the one-way valve (18) and apressing line (19) to a 3-way valve (17), the second connection of whichlies on the accumulator line (5) and the third connection of which lieson the tank line (8); the method comprising the step of operating thepressure converter (9; 9′) as a pressure intensifier or as a pressurereducer by (a) activating the three-way valve (17) and the prepressingvalve (11) to force the pressure converter (9; 9′) to act as a pressurereducer and to generate a first level of a pressure in the presscylinder (1); (b) activating the stop valve (15) and the main pressingvalve (14) to generate a predetermined second level of the pressure inthe press cylinder (1), the second level of the pressure being less thanor equal to a pressure in the pressure medium accumulator (7); (c)activating the main pressing valve (14) and the low-pressure chamberinlet valve (13) to force the pressure converter (9; 9′) to act as apressure intensifier and to generate a third level of the pressure inthe press cylinder (1), the third level of the pressure being greaterthan the pressure in the pressure medium accumulator (7); (d) activatingthe main pressing valve (14) and of the stop valve (15) to reduce thepressure in the press cylinder (1) to a fourth level of the pressure,the fourth level substantially equal to the pressure in the pressuremedium accumulator (7), and (e) activating the pressure relief valve(16) to reduce the pressure in the press cylinder (1) to the ambientpressure.
 13. A controller for a hydraulic press having a presscylinder, the controller comprising: a reservoir connectable to thepress cylinder and having a tank line; a hydraulic pump feeding anaccumulator line; a pressure accumulator connected to the accumulatorline; a pressure converter having a high pressure space and a lowpressure space provided with a high pressure line and a low-pressureline, respectively; and a valve group connecting the accumulator line,the high-pressure line, the low-pressure line, the cylinder and the tankline, the valve group comprising: a prepressing valve having one sideconnected to the low pressure space by the low-pressure line and anotherside connected to the press cylinder by a cylinder line, a low pressurechamber inlet valve connected between the accumulator line and the oneside of the prepressing valve, a low pressure chamber outlet valveconnected between the tank line and the low-pressure line, a mainpressing valve connected between the high pressure space and thecylinder line, the main pressing valve and the high pressure space beingconnected by the high pressure line, a stop valve connected between theaccumulator line and the high pressure line, and a three-way valveconnecting the accumulator line and the tank line to the high pressurespace through a nonreturn valve and the high-pressure line.
 14. Thecontroller of claim 13, wherein the pressure converter comprises a shafthaving opposite ends, a first pump coupled rigidly to one end of theshaft and configured to deliver a first specific volume, the first pumpbeing connected to the low-pressure line and having one side, whichbounds the low pressure space, a second pump coupled rigidly to theother end of the shaft and configured to deliver a second specificvolume, the first specific volume being greater than the second specificvolume, the second pump having one side connected to the high-pressureline, whereas the one side of the second pump bounds the high pressurespace.
 15. The controller of claim 13, wherein the pressure convertercomprises a converter cylinder, a piston rod displaceable in theconverter cylinder, a piston rigidly connected to the piston rod anddisplaceable therewith, the piston separating the low pressure space andthe high pressure space, the low pressure space being greater than thehigh pressure space.
 16. The controller of claim 13, wherein the valvegroup further comprises a pressure relief valve, the pressure reliefvalve having first and second sides connected to the cylinder line andto the tank line, respectively.
 17. The controller of claim 16 furthercomprising a control apparatus operative to electrically control openingand closing of the low-pressure chamber inlet valve, the low-pressurechamber outlet valve, the main pressing valve, the stop valve, and thepressure relief valve.